The maintenance of progenitor hematopoietic stem cells in culture is known to be dependent on the presence of a mixed population of stromal cells which provides an adherent layer upon which the stem cells reside and produces the different signals required for proliferation, self-renewal and differentiation of the hematopoietic stem cells into various hematopoietic lineages. Diverse cell types including stromal cells and adipocytes which arise from mesenchymal stem cells (MSCs) are present in bone marrow.
It is desirable in certain circumstances to maintain progenitor hematopoietic stem cells, such as CD34+ cells, in culture such that the cells proliferate and a majority of the cells retain their CD34+ phenotype.
It is further advantageous to maintain the hematopoietic stem cells such that, if differentiation does occur, differentiation will be along selected hematopoietic cell lineages, such as monocytes, osteoclasts or other cell types.